The electronic structure of phosphorane-iminato complexes of transition metals is studied by means of ab initio/DFT methods. Accordingly, the transition metal nitrogen bond is best described as an ionic interaction between a transition metal complex fragment and the strongly polarized NPH3- ligand. By elaborate MCSCF calculations a weak antiferromagnetic coupling of the four transition metal centers in the cubane core is predicted. This coupling can be represented by a simple Heisenberg Hamiltonian.